In general, heavy vehicles such as skid loaders, excavators, bulldozers, etc. have undercarriage that supports the vehicle and allows it to move to a desired position.
Typically, a crawler is used in the undercarriage for efficient transportation of a heavy vehicle on rough or unstable ground. Recently, a rubber crawler has been widely used to reduce vibration and noise during transportation and to minimize road damage.
Usually, the rubber crawler has a steel core inside the rubber track, and receives power from the transmission via a sprocket and an idler. But, with regard to an improvement in the flexibility of the rubber crawler and a reduction in vehicle weight, a coreless rubber crawler without a steel core is proposed.
FIG. 1 and FIG. 2 are front views of an undercarriage having such a coreless rubber crawler, with and without the crawler, respectively.
As seen in FIG. 1 and FIG. 2, the undercarriage is equipped with a coreless rubber crawler 10, a sprocket 20 for driving the rubber crawler 10, a track roller 50 located inside the coreless rubber crawler 10, and an idler 60.
The coreless rubber crawler 10 comprises a belt body having a closed-loop shape, pull lugs 11 formed on the outer surface of the belt body, and protruding teeth 12 formed on the inner surface of the belt body. The sprocket 20, which receives a rotational driving force from a main axle 40, has protruding cogs 21 on its outer circumference. As the cogs 21 are geared with the protruding teeth 12 on the inside of the coreless rubber crawler 10, the rotational driving force is transferred to the coreless rubber crawler 10 so that it moves forwards or backwards. The coreless rubber crawler 10 rotates with the track roller 50, located at the bottom of the coreless rubber crawler 10, and the idler 60 located at the rear, moving forwards or backwards and distributing the weight of the vehicle uniformly to the ground surface.
In such an undercarriage, the parts that bear the highest load are the cogs 21 where the sprocket 20 is geared with the coreless rubber crawler 10, and the point where the coreless rubber crawler 10 contacts the ground.
Some dynamic analysis research has been done on the point where the coreless rubber crawler 10 contacts the ground to determine the distribution of internal stresses thereabout. For example, Korean Patent Application No. 2002-0026894 (Rubber crawler and rubber crawler driving apparatus) reduces the difference in rigidity of a less rigid first lug part and a more rigid second lug part by lessening the thickness of the second lug along the belt body direction so it is smaller than that of the first lug part. As a result, deformation of the crawler is reduced, thereby reducing vibration and improving riding comfort.
On the other hand, there has been no dynamic analysis research at the cogs 21 where the sprocket 20 is geared with the coreless rubber crawler 10 (A–A′ in FIG. 1) to determine the distribution of the internal stresses thereabout.
Although there is the advantage of an improvement in the bending ability of the rubber crawler and a reduction of vehicle weight when a coreless rubber crawler 10 is used for the undercarriage, the coreless rubber crawler is difficult to equip and stress tends to be concentrated at specific points (see FIG. 3) because of the relatively small area at which the rubber crawler contacts the sprocket, which causes stress-induced deformation, leading to a reduction in life span and durability.
Accordingly, it is necessary to relieve stress at the contact points of the coreless rubber crawler and the sprocket in heavy vehicles like skid loaders, as friction between the vehicle and the ground is transferred to the rubber crawler, thereby reducing stress-induced deformation and improving the life span and durability.